The present invention relates to pellets of a chlorinated vinyl chloride resin (hereinafter referred to as "CPVC") compositon, pre-expanded particles and a process for preparing thereof, and more particularly to pellets of CPVC composition, pre-expanded particles prepared from the pellets and a process for preparing thereof for obtaining a foamed article having characteristics such that the foamed article generates little heat, produces little smoke and little poison gas and is hardly strained and cracked at burning, and further, has a large dimensional retention when an obtained foamed article is used in an atmosphere of high temperatures, i.e. the foamed article is excellent in heat resistance.
Since a CPVC has a large chlorine content, generates little heat and produces little smoke at burning, it is expected that the CPVC is employed as a heat insulating material having a high fireproofing property. However, a foamed article of the CPVC has a problem in fireproofing property, that is, the foamed article is largely shrunk when it is exposed in an atmosphere of high temperatures, for instance, in fire and the like. In order to prevent the foamed article. from shrinkage, it has been studied to contain a large amount of inorganic materials in the foamed article.
However, it has not yet been succeeded to get an excellent foamed CPVC article containing a large amount of inorganic materials by using the pre-expanded particles of the CPVC and the process for preparing thereof.
On the other hand, the melt-adhesion of the particles is lowered when the pre-expanded particles containing a large amount of the inorganic materials are subjected to an expansion molding in a mold because the inorganic materials existing on the surface of the particles act as an anti-blocking agent.
Besides, since the CPVC has a high softening temperature and requires high temperatures to give the excellent melt-adhesion of pre-expanded articles of the CPVC, a conventional molding machine used for the expansion molding of polystyrene or polyethylene can not be employed. Accordingly, there is a problem that a molding machine which is proof against high temperatures and high pressures which are usually generated from steam employed as a heat sourse should be specially equipped.
Still more, even though a large amount of the inorganic materials can be contained in the foamed article, there are some problems such that the residual stress and/or residual strain in the foamed article which are caused by the drawing of the resin during expansion are large. In such case, the shrinkage is generated due to the residual stress and/or the residual stain when the article is exposed in an atmosphere of high temperatures. That is, the shrinkage of the foamed article can not be minimized by containing the inorganic materials.
As the result of repeating earnest studies in order to solve the above-mentioned problems in the conventional process, there have been found the pellets of CPVC composition, the pre-expanded particles and the process for preparing thereof which are capable of solving the problems, and the present invention has been accomplished.